Fuselage mounted refueling systems contain several common components regardless of the particular installation, including: a hose reel assembly to store and dispense a refueling hose, a stowage tube or other piece of equipment which holds the hose-end components when the system is not in use and guide the hose between the hose reel drum and the exit point through the aircraft skin or outer mold line (OML). Also included is a tunnel or other fixed location exit point where the hose passes through the OML and into the airstream.
Currently deployed systems generally fall into one of two categories depending on whether the equipment is mounted in the fuselage or on a movable door or ramp. In the former instance, existing systems include a hose reel assembly in a fixed orientation and location inside the fuselage and a single fixed exit point is provided through the aircraft OML. In the latter arrangement, the hose reel and other components are mounted on a cargo door or ramp, moving together from the stowed position with the door or ramp closed into the refueling position when the door or ramp is lowered (opened).
The ramp/door arrangement is peculiar to roll-on/roll-off type systems which are temporarily installed in multi-role aircraft. On any system incorporating a hose and some sort of drum to wind it on and off, performance and reliability require that the hose remain tangential to the drum outside diameter during winding on/off. On the ramp type systems described above, the hose drum equipment and the stowage tube/hose exit components are all mounted to the ramp to maintain the tangency described regardless of the ramp position or movement.
A serious limitation inherent in such systems to date, however, is the capacity of the ramp to support the size and weight of the entire refueling system in flight and in use. Further performance limitations result from the lack of structural rigidity inherent in a moving door or ramp, such as increased vibration and high loads created by hose tension being applied to the ramp or door rather than solid aircraft structure like the cargo bay floor.